Fuel cells may be employed as a power supply for an increasing number of large-scale applications, such as materials handling (e.g. forklifts), transportation (e.g. electric and hybrid vehicles) and off-grid power supply (e.g. for emergency power supply or telecommunications). Smaller fuel cells are now being developed for portable consumer applications, such as notebook computers, cellular telephones, personal digital assistants (PDAs), and the like.
In a typical prior art fuel cell stack, electrons travel from the membrane electrode assembly (MEA) of a unit fuel cell through a separator plate to the MEA of the next unit cell. Typically, at each end of a fuel cell stack, current is supplied to or from an external circuit via connection components, including bus plates and connectors. Conventional fuel cell stacks may require numerous seals and the application of compressive force to prevent leakage of fuel and oxidant and to ensure good electrical contact between separator plates, MEAs and bus plates. Fuel cell stacks can therefore require many parts and assembly can be quite complex.
Fuel cells may also be connected in edge-collected configurations, such as planar configurations. In such fuel cell systems, current is collected from the edges of individual unit cells and travels in the plane of the fuel cells. In such fuel cell systems, the spatial arrangement of components may be different from the spatial arrangement of components in a conventional fuel cell stack. In such fuel cell systems, the predominant direction of electron flow may be different from the predominant direction of electron flow in a conventional fuel cell stack. In some of such fuel cell systems, the desired properties of components may be different from the desired properties of components in a conventional fuel cell stack.
Some edge-collected or planar fuel cell systems do not employ compressive force in order to maintain good contact between the fuel cell layer and various other components of the fuel cell system. In such fuel cell systems, components may be assembled and held in contact by other means. Accordingly, components that are employed in a conventional fuel cell stack for connection to an external circuit may not be optimal for employment in edge-collected fuel cell systems.
In a single fuel cell, minor electrical resistance from components can be relatively inconsequential. However, when multiple fuel cells are used, such as in a stack or planar fuel cell system, electrical resistance from components can accumulate to create a comparatively large internal resistance within the array. A large internal resistance can decrease performance of a fuel cell system with multiple cells, including a stack or planar fuel cell system.